The invention relates to a threshold circuit comprising a first field-effect transistor of a first conductivity type with a gate electrode, a source electrode and a drain electrode, a second field-effect transistor of a second complementary conductivity type with a gate electrode, a source electrode and a drain electrode, an input terminal connected to the gate electrodes of the first and the second field-effect transistor, an output terminal connected to the drain electrodes of the first and the second field-effect transistor, a first and a second power supply terminal connected to the source electrode of the first and the second field-effect transistor respectively, and first means for the application of a supply voltage between the first and the second power supply terminal.
Such circuits are, for example, known as inverters in logic circuitry. In such circuits the magnitude of the supply voltage also determines the dynamic range of the output voltage. Therefore it is desirable that the supply voltage is high relative to the threshold voltage of the transistors which are used, for example 10 V supply voltage relative to a threshold voltage of for example 1 V. However, it is then found that the input voltage swing, which is necessary to cause the output voltage to change from the one extreme value to the other extreme value, is also comparatively large relative to said threshold voltage, which renders these circuits less suitable for use as a threshold circuit, because then the threshold level is not accurately defined and the switching speed is limited.